Aluminum alloys are commonly used in turbocharger systems of internal combustion engines due to their lightness and ease of casting. More specifically, aluminum alloys are commonly used to form compressor wheels in single stage and multiple stage turbocharger systems. Cast aluminum alloys, however, may have limited fatigue properties, which necessarily limit turbocharger durability. Therefore, in some cases, aluminum compressor wheels may be forged rather than cast. Although forging results in the formation of a much stronger and more durable compressor wheel, the production costs are very high.
In addition, since the temperatures of compressed air can reach between about 200 and 250 degrees Celsius in some applications, these increased temperatures may have an adverse affect on later stage compressor wheels. At these increased temperatures, aluminum alloys, including cast and forged alloys, no longer retain the strength sufficient to meet the material property requirements for a compressor wheel of the turbocharger system. One such example of a cast aluminum alloy is shown in U.S. Publication 2005/0167009 to Shoji et al.
There are two commonly recognized approaches to addressing this problem. One such approach includes the use of a titanium alloy instead of an aluminum alloy to make the compressor wheel, as is taught in U.S. Pat. No. 6,588,485 B1 to Decker or U.S. Pat. No. 6,663,347 B2 to Decker et al. While the titanium alloy typically retains its material strength at temperatures up to about 500 degrees Celsius, the titanium alloy is denser than the aluminum alloy, which may lead to decreased turbocharger transient response. In addition, the titanium alloy costs significantly more than the aluminum alloy, leading to significantly higher production costs.
Another recognized approach is to utilize an intercooler between each stage of a multiple stage turbocharger system, such as described in U.S. Pat. No. 3,796,047 and U.S. Pat. No. 3,870,029, both to Crook et al., and U.S. Pat. No. 6,398,517 B1 to Choi. Specifically, the intercooler may reduce the failure of the compressor components, due to overheating, by decreasing the temperature of the air between each of the turbocharger system stages. This approach, however, increases both the complexity and volume of the multiple stage turbocharger system and drastically increases total costs. Therefore, there is a continuing need for compressor wheels, including both first stage and later stage compressor wheels, made from materials that are sufficient to meet all material property requirements, without drastically increasing the total costs of the turbocharger system.
The present disclosure is directed to one or more of the problems set forth above.